1. Field of the Invention
The present invention relates to power generation and heat utilization by an atomic energy, and in particular, to a reactor core cooling structure in a circular reactor core of a pebble bed high temperature gas reactor.
2. Description of the Related Art
A conventional pebble bed high temperature gas reactor is a high temperature gas reactor excellent in safety where a graphite ceramic coating is dispensed to small diametral and spherical nuclear fuel particles such as uranium dioxide in multiple layers, about 15,000 of the particles are collected and mixed with graphite powders and the like, and a spherical fuel (pebble fuel) sintered into a diameter of around 6 cm is used; and can supply a heat energy to a plant and the like by heating up a cooling gas to a high temperature of around 900 degrees Celsius with heat of a reactor core. As the cooling gas, helium or carbon dioxide is used.
Because in such the pebble bed high temperature gas reactor a temperature of the reactor core does not rise not less than 1600 degrees Celsius in any case, and a melting temperature of the graphite covering the fuel is 3,000 degrees Celsius, there is no worry about a melt down of the reactor core, so the reactor is excellent in safety. Therefore, for example, a containment vessel such as in a light water reactor also becomes unnecessary, a structure of a reactor is also simple, materials and parts need not to be custom-made articles for an atomic reactor, and thus articles for thermal power generation may result in being available, thereby a construction cost thereof being able to be markedly suppressed. Accordingly, a design development is progressing, including Japan, in the U.S., France, Germany, Holland, China, South Africa Republic, Russia, and the like.
As a utilization method of heat supplied from the pebble bed high temperature gas reactor, are being progressed studies such as using the heat for power generation with driving a turbine, and utilizing the heat for a thermo-chemical IS (Iodine-Sulfur) process that is a manufacturing method of hydrogen where a high temperature cooling gas is used.
As an example of such the pebble bed high temperature gas reactor, in claim 1 and FIG. 1 of Japanese Patent Laid-Open Publication No. 2000-505191 (hereinafter simply referred to as the patent document 1) is disclosed a pebble bed high temperature gas reactor where a cooling gas is introduced from a funnel-shaped bottom slant face, thereby fractions of a broken spherical fuel being prevented from clogging at an introduction part of the cooling gas.
In accordance with the pebble bed high temperature gas reactor described in the patent document 1 the cooling gas is designed to flow in a vertical direction toward an upper part of a reactor core from the introduction part of the cooling gas provided on the funnel-shaped bottom slant face.
However, in accordance with the pebble bed high temperature gas reactor described in the patent document 1 there is a problem as follows: When the cooling gas vertically passes through the reactor core as a rising flow, a pressure loss accounts for a large ratio of a total pressure loss, results in a large motive energy loss in carrying the cooling gas, and this results in depressing a heat efficiency of a total system thereof. Accordingly, in the pebble bed high temperature gas reactor it is requested to reduce the pressure loss of the cooling gas for cooling the reactor core.
In addition, although including the pebble bed high temperature gas reactor, the heat efficiency of a high temperature gas reactor becomes higher as a temperature of the cooling gas at an outlet of the high temperature gas reactor is raised, it results in being limited by a heat-resistant temperature of structural materials configuring the high temperature gas reactor. Generally, due to the heat-resistant temperature the temperature of the cooling gas at the outlet of the high temperature gas reactor is set 850 to 950 degrees Celsius. When making the cooling gas flow in from a lateral direction as in the pebble bed high temperature gas reactor of the present invention, an allowable maximum temperature of the cooling gas flowing out from cooling gas flow-out slits is decided by the heat-resistant temperature. However, because the temperature of the cooling gas at the outlet of the high temperature gas reactor becomes an average temperature where the cooling gas flowing out of the cooling gas flow-out slits is mixed, it is requested to make the temperature of the cooling gas flowing out of the cooling gas flow-out slits near the heat-resistant temperature on the whole, in order to heighten the temperature of the cooling gas at the outlet of the high temperature gas reactor till near the heat-resistant temperature. Accordingly, it is further requested to average the cooling gas flowing out of the cooling gas flow-out slits.